The present invention relates to a method of manufacturing an integrated circuit semiconductor device, and more particularly to a lithography step in which a check pattern of a resist film is formed on a semiconductor wafer to monitor a state of an element-forming resist pattern provided on the semiconductor wafer.
In the lithography step for forming polycrystalline silicon gates or wirings, for example, a polycrystalline silicon film is entirely deposited on a field insulating layer and on gate insulating layers covering a silicon substrate, and a positive resist film of 1.0 .mu.m to 2.0 .mu.m thickness is entirely coated on the polycrystalline silicon film. The resist film is selectively irradiated with ultra-violet rays through a step-and-repeat reductive exposure system (wafer stepper). By conducting a development, the element-forming resist pattern is formed. Next, the polycrystalline silicon film is selectively etched by using the element-forming resist pattern as a mask, and the polycrystalline silicon gates and wirings are formed. In this case, if the shapes of the gates and wirings is incorrect caused by a bad element-forming resist pattern, the re-work is impossible no more. Therefore, before the etching process, the element-forming resist pattern must be checked to determine whether it has a desirable pattern or not. A desirable resist pattern is ought to be obtained if a precise optical mask or a precise reticle mask is used in the exposure process of ultra-violet rays. However, in practice, sometimes a resist stripe in the pattern is unfavorably contacted to a neighbor resist stripe, or else the resist stripe becomes unfavorably narrow width. These phenomena are caused by an undesirable amount of ultra-violet rays and/or conditions of the development, and therefore, they are monitored by providing a check pattern of the resist film. The check pattern and the element-forming resist pattern are simultaneously formed on the semiconductor substrate. Therefore, the state of element-forming resist pattern caused by conditions of exposure and development can be monitored by checking the check pattern with eyes of a worker. When the predetermined shape of the check pattern is not obtained, the resist film pattern including the element-forming pattern and the check pattern is removed to conduct a re-work of coating a new resist film, performing selective exposure of ultra-violet rays and development once more.
A check pattern in a prior art has a plurality of stripes arrayed in parallel, the width of each stripe and the interval between the stripes being designed to be equal.
If all intervals in the element-forming resist pattern are designed to be 2.0 .mu.m or more, the check pattern of the resist can be designed such that the interval between the resist stripes in the check pattern substantially coincides with a minimum interval in the element-forming resist pattern, and when the interval in the check pattern is formed after development it can be confirmed that the minimum interval in the element-forming resist pattern would be formed without any unfavorable left resist part.
However, if the interval becomes 1 .mu.m or less, the width of the resist stripes at both sides of the interval has an effect on the formation of the interval in the resist pattern. More particularly, when the width of the resist stripes is designed to be broad and the interval between the stripes is designed to be 1 .mu.m or less, sometimes unfavorable resist part is left at the interval portion to short the resist stripes after development.
Therefore, even if a check resist pattern which is designed such that a plurality of resist stripes of 0.9 .mu.m width are arranged in one direction with each constant interval of 0.9 .mu.m is correctly formed after the development, an element-forming resist pattern which is designed such that two of resist stripes of 2.0 .mu.m width for forming wirings or electrodes extend with a constant interval of 0.9 .mu.m is sometimes not correctly formed after the development because the resist is left at the interval in the element-forming resist pattern and cannot be completely removed during the development. Thus, a part of resist is sometimes left to bridge the neighbouring two resist stripes. In that case, the check resist pattern in the prior art no more serves to monitor the state of the element-forming resist pattern. The true cause of this phenomenon has not been found yet. However, it could be supposed that when wide resist stripes are to be provided with a narrow interval of 1 .mu.m or less, the lack of the flow of the developing solution occurs at the interval portion where the resist is to be removed and the resist is not completely removed from the interval portion.